As computer-based systems advance in sophistication and proliferate in number, associated service problems increase in novelty and number as well. Elevators provide a representative example. In the prior art, elevator problems that exist at the time a service technician requests this information can be extracted by an Operator's Maintenance Tool (OMT), as disclosed in U.S. Pat. No. 4,561,093 to Doane et al. With the OMT, a user must either ask the elevator controller for the diagnostic status, or command the elevator to operate in an attempt to duplicate and identify the problem. This works well for simplistic elevator control problems However, for more complex elevator problems, it is often required to install a complex and expensive logic state analyzer on the computer-based elevator controller to diagnose the aforementioned problems. However, the analyzer must be operated by a person knowledgeable with the control software of the elevator controller. Normally, this is not the elevator service technician.
To solve this problem, enhanced elevator diagnostics were developed. Commonly-owned U.S. Pat. No. 4,750,591 to Coste et al. discloses a method and apparatus for monitoring an elevator by utilizing signals available within the elevator itself to determine the identity of an elevator car operating state. That art is predicated on the fact that an elevator car normally operates sequentially from state to state in a closed loop sequential chain of linked normal operating states. As a result, selected message signals are provided in the presence of state transitions to either normal or abnormal operating states. These selected message signals are intended to be transmitted to external monitoring apparatus at the elevator site.